The present invention is directed to a portable, internal combustion powered work device, such as a device for setting fastening elements into a receiving material including an axially extending combustion chamber for receiving an air fuel mixture to be ignited therein. An axially extending guide cylinder is located within and axially displaceable relative to the combustion chamber and an axially extending piston is displaceably guided in the guide cylinder.
Such a work device is disclosed in U.S. Pat. No. 4,759,318.
This known work device has a cylindrically shaped combustion chamber divided into a rear partial combustion chamber and a front partial combustion chamber relative to the setting direction. The chambers communicate with one another via a check valve which permits flow from the rear chamber to the front chamber. Front partial combustion chamber has a central opening on its front side covered by a differential piston which encloses the combustion chamber coaxially at the outside. When an air-fuel mixture is ignited in the combustion, chamber the differential piston moves forwardly away from the combustion chamber and compresses the air located in front of it, the air is stored in a supply tank. The compressed air is used, on one hand, for moving the piston rearwardly, since the vacuum pressure required for such movement, which is already present in the combustion chamber, is not sufficient due to the combustion residues present in the chamber, and on the other hand, for the required opening of the check valve by means of a tappet, as well as for opening an exhaust gas duct for flushing the combustion chamber. Flushing the combustion chamber is effected by air sucked in above the differential piston and pressed into the combustion chamber through a flushing duct located between the combustion chamber and the differential piston as the piston is guided rearwardly. After completion of the rearward guiding of the differential piston and the flushing of the combustion chamber, the exhaust gas duct is closed and the combustion chamber receives compressed air from the supply tank flowing through the flushing duct. Since the combustion chamber has received a new supply of fuel, an air-fuel mixture is now located in the combustion chamber and can be ignited for again moving the differential piston.
As mentioned above, the combustion residues are flushed from the combustion chamber by an additionally produced air flow, accordingly, a flushing gas volume is required which is greater than the combustion chamber volume, since the interior of the differential piston must be flushed first. Therefore, this known work device requires a relatively large volume and a complicated air flow flushing system.